0、导读

在slave上，发现SQL thread长时间处于Opening tables状态

1、问题描述

朋友的数据库，做了主从replication复制。在slave实例上，SQL thread的长时间处于Opening tables状态，复制进程异常。

mysql> show processlist;

+----+-------------+-----------+------+---------+-------+----------------------------------------+------------------+

| Id | User | Host | db | Command | Time | State | Info |

+----+-------------+-----------+------+---------+-------+----------------------------------------+------------------+

| 1 | system user | | NULL | Connect | 554 | Queueing master event to the relay log | NULL |

| 2 | system user | | NULL | Connect | 59212 | Opening tables | NULL |

整个实例大概20个database，总共300G左右。

master是5.5版本，slave是5.6版本，master上执行xtrabackup全库备份后搭建的slave。

2、原因分析

我的第一反应是table cache是不是太小了，导致open table比较慢，所以才长时间处于这个状态。无论如何，先一层层排查吧。

先看下slave status（部分无用信息我隐掉了）：

mysql> show slave status\G

*************************** 1. row ***************************

Slave_IO_State: Queueing master event to the relay log

Master_Log_File: master-bin.000618

Read_Master_Log_Pos: 614915856

Relay_Log_File: replicate.000008

Relay_Log_Pos: 2384117

Relay_Master_Log_File: master-bin.000617

Slave_IO_Running: Yes

Slave_SQL_Running: Yes

Replicate_Do_DB:

Replicate_Ignore_DB:

Replicate_Do_Table:

Replicate_Ignore_Table:

Replicate_Wild_Do_Table:

Replicate_Wild_Ignore_Table:

Last_Errno: 0

Last_Error:

Skip_Counter: 0

Exec_Master_Log_Pos: 252048331

Relay_Log_Space: 1438994074

Until_Condition: None

Until_Log_File:

Until_Log_Pos: 0

Seconds_Behind_Master: 59240

Master_SSL_Verify_Server_Cert: No

Last_IO_Errno: 0

Last_IO_Error:

Last_SQL_Errno: 0

Last_SQL_Error:

Replicate_Ignore_Server_Ids:

Master_Server_Id: 1

Master_UUID:

Master_Info_File: /home/mysql/master.info

SQL_Delay: 0

SQL_Remaining_Delay: NULL

Slave_SQL_Running_State: Opening tables

Master_Retry_Count: 86400

Last_IO_Error_Timestamp:

Last_SQL_Error_Timestamp:

Master_SSL_Crlpath:

Retrieved_Gtid_Set:

Executed_Gtid_Set:

Auto_Position: 0

看不出来有什么异常的。

再看下系统负载情况：

[root@localhost mysql]# vmstat -S m 1

procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----

r b swpd free buff cache si so bi bo in cs us sy id wa st

0 2 1 19591 458 230576 0 0 11 20 0 0 0 0 100 0 0

1 1 1 19587 458 230579 0 0 2032 2528 1645 584 1 1 93 4 0

1 1 1 19583 458 230582 0 0 1664 2712 1773 461 1 1 93 4 0

0 2 1 19578 458 230585 0 0 2080 3376 1810 660 1 1 93 4 0

2 0 1 19576 458 230587 0 0 2224 1804 1634 594 1 1 94 4 0

3 1 1 19569 458 230590 0 0 1968 3488 1693 566 1 1 93 4 0

1 1 1 19567 458 230593 0 0 2016 2632 1775 515 1 1 93 4 0

[root@localhost mysql]# sar -d 1

Linux 2.6.32-431.el6.x86_64 (localhost.localdomain) 03/21/2015 _x86_64_ (24 CPU)

03:21:57 PM DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util

03:21:58 PM dev8-0 185.86 5753.54 64.65 31.30 1.20 6.48 5.08 94.44

03:21:58 PM DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util

03:21:59 PM dev8-0 197.03 6114.85 95.05 31.52 1.16 5.88 4.48 88.32

03:21:59 PM DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util

03:22:00 PM dev8-0 188.89 5882.83 88.89 31.61 1.14 6.03 5.09 96.16

03:22:00 PM DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util

03:22:01 PM dev8-0 166.00 5152.00 80.00 31.52 1.42 8.56 5.58 92.70

也看不出来异常，继续看看mysql的日志吧：

2015-04-21 14:51:04 18667 [ERROR] Native table 'performance_schema'.'objects_summary_global_by_type' has the wrong structure

2015-04-21 14:51:04 18667 [ERROR] Incorrect definition of table performance_schema.rwlock_instances: expected column 'WRITE_LOCKED_BY_THREAD_ID' at position 2 to have type bigint(20), found type int(11).

2015-04-21 14:51:04 18667 [ERROR] Native table 'performance_schema'.'setup_actors' has the wrong structure

2015-04-21 14:51:04 18667 [ERROR] Native table 'performance_schema'.'setup_objects' has the wrong structure

2015-04-21 14:51:04 18667 [ERROR] Native table 'performance_schema'.'table_io_waits_summary_by_index_usage' has the wrong structure

2015-04-21 14:51:04 18667 [ERROR] Native table 'performance_schema'.'table_io_waits_summary_by_table' has the wrong structure

2015-04-21 14:51:04 18667 [ERROR] Native table 'performance_schema'.'table_lock_waits_summary_by_table' has the wrong structure

2015-04-21 14:51:04 18667 [ERROR] Column count of mysql.threads is wrong. Expected 14, found 3. Created with MySQL 50524, now running 50623. Please use mysql_upgrade to fix this error.

2015-04-21 14:51:04 18667 [ERROR] Native table 'performance_schema'.'events_stages_current' has the wrong structure

2015-04-21 14:51:04 18667 [ERROR] Native table 'performance_schema'.'events_stages_history' has the wrong structure

2015-04-21 14:51:04 18667 [ERROR] Native table 'performance_schema'.'events_stages_history_long' has the wrong structure

…

…

2015-04-21 15:05:17 7f5997fff700 InnoDB: Error: Table "mysql"."innodb_table_stats" not found.

2015-04-21 15:05:17 7f5997fff700 InnoDB: Error: Fetch of persistent statistics requested for table "db_anonymous_info_10"."t_friend_info_3" but the required system tables mysql.innodb_table_stats and mysql.innodb_index_stats are not present or have unexpected structure. Using transient stats instead.

2015-04-21 15:05:17 7f7beb0cd700 InnoDB: Error: Table "mysql"."innodb_table_stats" not found.

2015-04-21 15:05:17 7f7beb0cd700 InnoDB: Error: Fetch of persistent statistics requested for table "db_user_trade_1"."t_trade_15" but the required system tables mysql.innodb_table_stats and mysql.innodb_index_stats are not present or have unexpected structure. Using transient stats instead.

可以看到，这个实例中，P_S（performanc_schema）库的几个表结构都异常了。另外，mysql.innodb_table_stats表也异常了，导致InnoDB表数据收集异常，然后SQL thread也跟着异常了。

3、问题解决建议

造成上面问题主要原因是，没有用正确的方式来部署slave实例。从master上用xtrabackup物理备份到slave，启动实例后，应该再执行 mysql_upgrade 升级相关表结构，确保P_S（performanc_schema）、I_S（information_schema）以及 mysql 等几个系统库表结构都升级到最新版本。